The theology of excommunication holds that bishops don’t actually excommunicate people: they simply declare that a person who claims to be Catholic but acts contrary to Catholic belief in a public way has already severed his or her ties to the Church. Bishops make this fact public to bring the culpable party to his or her senses in the hope he or she may repent from what they have done to themselves. An additional effect of speaking out publicly is that it strengthens the faithful.
The difficulty is that the majority of bishops refuse to carry out their part because they are divided on the issue. Instead of being publicly rebuked, Pierre Trudeau received a tremendous funeral broadcast nationally. Cardinal O’Malley of Boston went Cardinal Turcotte of Montreal one better by giving the renegade Catholic Ted Kennedy a nationally televised funeral with two priest-homilists declaring him to be in heaven! (Source)
Excommunication: the boogey-man of the Catholic Church.